1. Field of the Invention
The present invention relates generally to ocular medical instruments and, more specifically, to safety net instruments for use in cataract surgery.
2. Discussion of the Related Art
During their lifetimes, many people become afflicted with cataracts, i.e. lenticular opacities that interfere with vision. Indeed, cataracts may be considered the most prevalent visually disabling eye disease in the world. The cloudiness or opacity associated with cataract arises in the nucleus of the anatomical lens, which includes a lens capsule also known as the capsular bag, the nucleus within the lens capsule, and gelatinous cortical material between the nucleus and the lens capsule. Currently, the only effective treatment for cataract is surgical removal of the cataract from the eye.
One method for surgical removal of a cataract is intracapsular cataract surgery or extraction, which involves removing the entire anatomical lens including the lens capsule. The lens capsule is removed essentially intact, with the cataractous nucleus contained therein. Intracapsular cataract surgery has numerous disadvantages including the need for undesirably large incisions to accommodate the lens capsule as it is withdrawn from the eye, prolonged recovery times, the risk that the vitreous body, normally contained behind the posterior capsular wall, may move forward into the anterior chamber of the eye, and potential complications including retinal detachment, cystoid macular edema, glaucoma, corneal decompensation and/or uveitis. Following intracapsular cataract surgery, vision is typically restored in the patient with corrective eye glasses or contact lenses, since the absence of the lens capsule makes it difficult for an intraocular lens implant to be properly supported in the eye.
Another method for surgical cataract removal is extracapsular cataract surgery or extraction. Extracapsular cataract surgery involves making an opening in the lens capsule and removing the nucleus and cortical material from the lens capsule, with the posterior capsular wall ideally remaining in place within the eye to inhibit movement of the vitreous body into the anterior chamber and to facilitate positioning of an intraocular lens implant. In extracapsular cataract surgery, the nucleus, which may be quite dense and hard particularly in the case of a mature cataract, is typically fragmented or broken up into smaller pieces, thereby allowing removal through a relatively small incision. The nucleus may be broken up or fragmented employing various fragmentation techniques and fragmenting instruments using, for example, mechanical, laser, electromagnetic or ultrasound energy. A preferred fragmentation technique is phacoemulsification, in which a fragmenting instrument delivers ultrasound energy to fragment or break up the nucleus, and the resulting nuclear fragments or pieces are typically removed from the eye by suction or aspiration through the fragmenting instrument.
Although extracapsular cataract surgery is usually preferred over intracapsular cataract surgery, extracapsular cataract surgery presents the risk that the posterior capsular wall may be ruptured inadvertently, such as due to unintended contact with the fragmenting instrument and/or due to the suction used to remove the nuclear fragments. Rupture of the posterior capsular wall during extracapsular cataract surgery gives rise to many of the same disadvantages associated with removal of the lens capsule in intracapsular cataract surgery. Particularly, mixing of nuclear material with the vitreous body may manifest as uveitis, resulting in an inflammatory reaction in the eye. A vitrectomy may be necessary to remove nuclear fragments or pieces from the vitreous body; however, a vitrectomy itself has potential adverse consequences, including retinal complications, for the patient. Complete removal of the nuclear material from the vitreous is difficult to accomplish; and, if all of the nuclear fragments or pieces are not removed, the patient is at risk for various complications including cystoid macular edema, glaucoma, corneal decompensation and uveitis. Often, removal of these fragments requires a secondary procedure by a retinal specialist, at considerable cost to the patient and/or third party payer.
It has been proposed to shield the lens capsule to protect against damage during surgical cataract extraction, but not to collect migrating nuclear fragments after the occurrence of a capsular rupture, as disclosed in U.S. Pat. No. 5,676,669 to Colvard. Colvard discloses a foldable, soft shield for being placed within the lens capsule between the nucleus and the posterior capsular wall prior to removing the nucleus during cataract surgery. The shield is placed in the lens capsule as a matter of course prior to fragmentation of the nucleus to protect the posterior capsular wall against possible damage. Since damage to the posterior capsular wall is not an inevitable occurrence during cataract surgery, the patient may be unnecessarily placed at increased risk from the shield being routinely inserted in the lens capsule. The shield, which is solid, has elastic memory biasing it to an expanded configuration. A relatively large incision is required to insert the shield in the eye in the expanded configuration. The shield must be deformed and then positioned within a rigid insertion cylinder for insertion of the shield in the eye through a smaller incision. The shield is ejected entirely from an end of the insertion cylinder into the lens capsule such that the shield is free and unattached within the lens capsule. The surgeon thereafter has no control over the shield as it automatically assumes the expanded configuration upon ejection from the insertion cylinder. The insertion cylinder is longitudinally straight and cannot be positioned around the nucleus to afford better control over shield position behind the nucleus. Regardless of whether the shield is in the expanded configuration or the collapsed configuration during insertion in the eye, the shield must follow the contour of the relatively denser and harder nucleus to randomly arrive at a position between the nucleus and the posterior capsular wall. Accordingly, the shield must be inserted in the eye prior to removal of the cataractous nucleus, and is not suited for insertion in the eye where some of the nucleus has already been removed. In order to remove the shield from the eye, the shield must be grasped with an instrument and pulled either into a withdrawal cylinder or directly through the incision. Grasping the shield with an instrument is tedious and time consuming and may require numerous trial and error attempts. Since the shield is solid, undesired pressure imbalances or differentials in the eye may occur due to there being no air or fluid flow through the shield.
Baskets or nets have been proposed for enclosing a cataractous nucleus and removing it from the eye as represented by U.S. Pat. No. 5,891,153 to Peterson and U.S. Pat. No. 3,908,661 to Kramer. Peterson discloses a basket for enclosing a cataractous nucleus, which is crushed by retraction of the basket into a tubular member and advancement of an auger into the interior of the basket. The basket is not collapsible in order to assume a narrow profile. The basket can be placed around the nucleus only by virtue of the nucleus being previously prolapsed into the anterior chamber of the eye or positioned so that one pole of the nucleus is above the anterior capsular wall. The nucleus must be directed into the basket using separate instruments. Kramer discloses a net having a self-expanding frame that is movable from a collapsed condition to an expanded condition automatically upon extension of the frame from a sleeve. Kramer requires that the nucleus be freed into the anterior chamber of the eye in order to be positioned in the net. The net containing the captured nucleus is retracted into the sleeve for removal of the nucleus from the eye, the nucleus being crushed by the net and the sleeve as the net is retracted. A major portion of the nucleus is squeezed outwardly through openings in the net and undesirably fall as fragments into the eye. These fragments must thereafter be removed by another procedure.
The need exists for a lenticular net that is positioned, as needed, between the nucleus and a ruptured capsular wall which occurs or may occur during cataract surgery subsequent to initiating fragmentation and aspiration of the nucleus, that is mechanically constrained in a contracted or collapsed configuration for insertion in the lens capsule through a small incision, that is controllably guided during insertion via a handle while constrained in the contracted configuration, that is mechanically moved to and maintained in an expanded configuration behind the nucleus to prevent or block migrating nuclear fragments or pieces from passing through the ruptured capsular wall while fragmentation and aspiration of the nucleus continue, that is mechanically returned to the contracted configuration for withdrawal from the eye subsequent to completion of fragmentation and aspiration, that remains attached to and controlled by the handle during insertion and withdrawal, and that permits flow therethrough while preventing the passage therethrough of migrating nuclear fragments.